Malaria is still a major public health problem in Africa despite the continuous deployment of interventions within the region. Vector control is one of the important strategies being used in the fight against malaria. These efforts include large-scale distribution of long-lasting impregnated nets (LLINs) and indoor residual spraying (IRS). Although these control measures have been successful in reducing malaria incidence since its initial scale-up in early 2000s, within the last few years there has been resurgence of malaria incidence in most parts of Africa, including Kenya. One of the factors that has been implicated in this malaria resurgence is insecticide resistance. The increased use of insecticide-based malaria vector control tools in the past decade have placed greater selection pressure on malaria vector populations resulting in higher rates of the incidence of insecticide resistance tha is likely to impact on the effectiveness of vector control. Despite increased control efforts, ther is evidence of limited impact and a resurgence of clinical malaria in parts of sub-Saharan Africa including Kenya. There is also evidence of shifts in vector behavior and species composition. There is pressing need to develop viable insecticide resistance management strategies. These strategies are predicated upon better understanding of the effects of insecticide resistance on vector behavior and fitness. The overall objective of this application is to determine the effect o insecticide resistance on the behavior and fitness of the main malaria vectors of Sub-Saharan Africa, Anopheles gambiae, An. arabiensis and An. funestus, and their impact on malaria transmission in Kenya. The long-term objective is to determine the changes in the ecology of malaria vector species during the period of most intensive malaria intervention programs in Africa. I have designed 3 specific aims to achieve this objectives. This will be the first study tht will analyze and quantify behavioral resistance in the three main major malaria vector species in Africa using different insecticides. In Aim 1, we will determine how evolution of insecticide resistance in vector mosquitoes affects their feeding and resting behavior. Insecticide resistance could affect mosquitoes to adapt behaviorally and therefore change from feeding indoors to outdoors and resting outdoors because of pressure from the use of LLINs and IRS, which are indoor based. These behavioral changes will likely affect vector potential to transmit malaria. Aim 2 will test how insecticide resistance in vectors affects their fitness for development, survivorship, reproductive potential and infectiousness. The actual cost of the fitness needs to be studied to understand how the development of resistance affects the vectorial capacity of these vectors. Aim 3 is to predict and validate the consequences of insecticide resistance on malaria transmission which is important in helping policy makers to better parameterize models that guide malaria interventions. Results from this study will help understand the mechanisms for malaria resurgence in Africa, help to come out with better strategies to manage insecticide resistance in malaria vectors and help in coming up with models for malaria vector control.